An app detailing the basics of life support. How to perform some of the most basic life saving techniques should you have no option but to use them e.g. Friend/Family member falls seriously ill up a mountain.
Having done BLS training it quickly became apparent to me that there was no way I'd remember how many chest compressions are required vs breaths for an adult/child/baby, etc. My solution? Take a picture on my mobile phone of the flow chart the trainers drew during the training with the stages involved and the number of compressions vs rescue breaths.
Thus an app, moving though the various stages (e.g. starting with "Is it safe to administer BLS") going on to show animations of things like the correct way to move someone into the recovery position etc could be of use in an emergency.
It'd be nice if it was avaliable on Blackberrys & Android phones too given the size of their user bases!